1. Field of the Invention
The invention pertains to an attitude control system wherein a pitch angle and horizontal pitch combine to determine a parallel path of travel of a connected member with respect to a horizontal reference plane. More particularly the invention relates to an attitude control system for earth moving machines and, specifically to the control of the attitude of the digging implement.
2. Description of the Prior Art
Various control systems for determining the attitude of the path of travel of an object are the subject matter of a number of prior art references. The present control system pertains not only to a means for controlling the path of travel of an object with respect to a horizontal reference but also means for controlling a horizontal pitch angle, the combination of which determines the path of travel of a connected member with respect to a horizontal reference.
Control systems wherein a path of travel of a connected member are monitored or controlled by pitch angle and horizontal pitch have generally been controlled by horizontal pitch control alone. However in many applications it is necessary to monitor, process and control both pitch angle and horizontal pitch in order to achieve the advantages of an improved system. It will be recognized that such control systems are applicable to aircraft, vehicles and heavy earth moving machinery.
Earth moving machinery such as automated trenching machines have found particular usefulness in digging drainage ditches. In addition to the digging function, typical trenching machines may also lay drainage tile or pipe in the bottom of the ditch to facilitate drainage. Various forms of earth moving and digging implements are used which can be controlled by the present invention. One form of digging implement may consist of an endless chain carrying a plurality of digging scoops or shovels and supported by a boot. Despite the particular type of trencher such as, plow, or chain the digging implement is hinged to the trencher and terminates in a support boot that rests on the bottom of the ditch which is being excavated.
A laser system or other means is generally employed as a horizontal pitch reference for a reference plane to establish the desired attitude for a ditch. The current state of the art employs a laser beam as a horizontal reference in which the laser control system senses that the digging arm is cutting a ditch deeper than that established by the reference plane, it increases the up attitude of the bottom of the boot supporting the digging. An increasing up attitude of the boot of the digging arm tends to allow the digging arm to plane up out of the ditch. In normal operation the digging arm will not ride up completely out of the ditch but will level off at a depth depending upon the final attitude established by the laser reference of the boot supporting the digging arm. Likewise, if the laser sensing system determines that the depth of the ditch being dug is too shallow as determined by the reference plane, it will decrease this up pitch tending to cause the digging arm to dig itself deeper into the ditch.
Operators of such trenchers have experienced problems maintaining a uniform ditch attitude when the consistency of the soil being excavated changes. For example, if the digging arm of a trencher which had previously been digging dirt reaches a sandy portion of the earth, the boot finds less support than it did when the digging implement was digging dirt. As a result, a digging arm drops down and the laser referenced grade control then increases the planing angle of the bottom of the boot, i.e. lowers the trailing edge of the boot. Since the laser reference receiver is on a line above the front of the boot, this increased angle results in the trailing edge of the boot being significantly lower than the reference plane established by the laser and sensed by the laser receiver. Therefore, the depth of the ditch can be several inches deeper than desired. In the opposite case, where soil becomes hard to penetrate, the digging arm tends to rise up out of the ditch. The laser referenced grade control reacts by decreasing the up planing angle of the bottom of the boot. The laser mast supporting the laser receiver, which had been in a substantially vertical orientation, is now tilted forward so that the receiver is lowered toward the front of the digging arm and senses the digging arm below the reference plane even though the bottom of the boot is too high. In this case, the ditch will be shallower than desired.
The laser grade control systems have controlled the grade cylinders of such trenching machines for controlling the grade of the digging arm. It has been known that the lift cylinders of such trenching machines may be manually controlled for correcting the attitude of the digging arm when changes in soil consistency are encountered. However, no one has heretofore known how to automatically compensate for the changes in the altitude of the ditch being dug as a result of changes in soil consistency.